1. Field of the Invention
The present invention relates to a mobile communication control method, and a radio network controller, for use in a mobile radio network providing a multicall service.
2. Description of the Related Art
W-CDMA (Wideband Code Division Multiple Access) is one of the communication schemes defined in IMT-2000, the international standard for third generation mobile telephone systems.
As shown in FIG. 1, a W-CDMA mobile network comprises mobile stations (MSs), radio base stations (NodeBs), radio network controllers (RNCs), and a mobile switching center (circuit switched: MSC, packet switched: SGSN).
As a third generation mobile communication system, W-CDMA not only supports traditional voice communication services, but also provides multimedia mobile communication services, plus global roaming services that enable customers to use their mobile stations (mobile telephones) in various parts of the world. Further, “multicall” that enables packet data transmission to be performed concurrently with voice communication, which has not been feasible with PDC (Personal Digital Cellular), is also supported with this service, it becomes possible, for example, to transmit graphs or diagrams for presentation purposes while carrying on business negotiations over a voice communication link. In this case, a plurality of codes (radio resources) are allocated to the mobile station, so that the voice data and information data, each spread by a corresponding one of the plurality of codes, can be transmitted and received using the same frequency.
FIG. 2 shows the configuration of a radio network controller (RNC). In FIG. 2, a call processing section 10 controls a plurality of radio base stations (NodeBs) via a NodeB interface section 12 and a CN interface section 14, and performs incoming/outgoing call connection control, call termination control, and diversity handover control such as the selecting and combining of signals arriving from the same mobile station via a plurality of NodeBs and the distribution of replicas to the plurality of NodeBs; in addition, the call processing section 10 incorporates the function of a resource usage managing section 18 which, when performing incoming/outgoing call connection control, for example, seizes necessary radio resources between the RNC and the NodeBs by referring to a resource database section 16.
As described above, in the implementation of multicall in the prior known mobile communication system, if a new packet call connection is to be set up during a voice communication call, a procedure becomes necessary for the radio network controller (RNC) to seize a new radio resource for the packet call and to set up a radio bearer. This procedure involves adding a PS (Packet Switched) service to the call to which a CS (Circuit Switched) service is being provided, but this can cause the following problems.
1) In the prior art, there is a need to seize a new radio resource when setting up a packet communication call but, during this process, a radio resource seizure error or a link connection error may occur.
2) When adding a packet communication connection to a voice communication connection already established, a finite time is required for processing such as the resource seizure for the PS call, and this can affect the PS call connection which is more time critical.
The effects of these problems will be described by taking an example. Suppose, for example, that, when a customer is communicating by voice with a call center of a mail-order house, the customer requests the call center to transmit image data as he desires to view the details of merchandize; in this case, at the present state of technology, a radio resource seizure error may occur during the PS call setup, resulting in unsuccessful data communication or an inability to transmit more time-critical data because of the time required for connection of a data communication channel, and thus missing a business opportunity. A failure in data communication or a delay in communication time can cause a serious problem in such cases as stock dealing in which prices can greatly vary as the time elapses.
Depending on the functions of the mobile station (MS), the PS connection can be established simultaneously with the CS connection, but this involves the problem that resources from the RNC to the core network (CN), where seizure errors are less likely to occur, are needlessly seized.